Carbonizing metals for radio tubes



July 19, 1938. c. EDDISON ET AL 2,124,162

CARB NIZING METALS FOR RADIO TUBES Filed March 27, 1957 1/ Mel! EM/L G. W/DELL ATTORNEY INVENTORS CLIFFORD EDD/SUN AND Patented July 19, 1938 UNITED STATES PATENT ()FFICE CARBONIZING METALS FOR- RADIO TUBES ware Application March 27, 1937, Serial No. 133,310

6 Claims.

This invention relates to a method and means for carbonizing metals and more particularly to carbonizing metal parts, such as electrodes, for use in the manufacture of radio tubes.

In the radio tube art carbonized grid and plate electrodes have many advantages; for example, a carbonized electrode radiates heat more efficiently and operates at a substantially lower temperature than a clean metal electrode for the same wattage input, and its secondary electron emission is much lower, as a carbonized electrode is inherently a poor emitter of electrons.

In one method of carbonizing metal, such as nickel, for use in electron discharge tubes, the metal parts are heated for one or two hours to a temperature of about 900 C. in an atmosphere of a carbon bearing gas free from air to deposit a coating of carbon on the metal parts, probably by some reaction between the metal and carbon vapors. Electron discharge tubes made with oxide coated cathodes and metal parts carbonized in an atmosphere of hydro-carbon gas, such as methane, propane, or butane have been found in some cases to have low cathode emission and to contain inadmissible quantities of gas.

The object of this invention is to provide an improved method and means for carbonizing and treating metal parts for use in electron discharge tubes. 1

In accordance with one embodiment of this invention, the tube parts are preformed and carbonized in the usual way and then treated by being placed in a furnace and heated for about 90 minutes to a temperature below the temperature at which water vapor decomposes to yield oxygen, while steam is passed through the furnace. Preferably, the parts are then maintain-ed at a temperature between 100 and 150 C. in steam before their removal for use. Alternatively, strip metal from which tube parts are made may be continuously carbonized and steam treated. It has been found that this treatment causes a marked improvement in the quality of electron discharge tubes made with metal par-ts so treated, the tubes having better cathode emission and lower gas content and longer useful life. It is believed that in the cooling chamber through which the carbonized metal parts must necessarily pass in leaving the carbonizing chamber, impurities, such as products of decomposition of the gases, are absorbed by the carbonized parts, and that these products of decomposition, which may be naphthalene, sulphur, tar, or light oils, while present in very small amounts, are sometimes svificient to impair the operation of a radio tube containing the parts, either by rendering the tube low in electron emission or possibly high in gas content. Apparently the steam serves not only to mechanically carry away the undesired by-products of the hydrocarbon gas that are volatile at less than 350 C., but also functions chemically to render volatile at that temperature hydrocarbons which are normally adsorbed on the carbon coating. The maximum temperature of about 350 C. is apparently fixed by the temperature at which oxygen is produced in the chamber, which, it has been found, destroys the carbon coating and oxidizes the metal.

The invention will now be explained more in detail with reference to the accompanying drawing in which:

Figure 1 is a perspective View, partly in section, of one device embodying this invention;

Figure 2 is a longitudinal sectional view of the device of Figure 1;

Figure 3 is a View of a carrier for tube parts to be treated in the device of Figures 1 and 2, according to this invention;

Figure 4 is a view of a furnace accessory comprising a disc assembly employed in the improved furnace of this invention; and

Figure 5 is a View of a device for continuously treating a strip of carbonized metal according to this invention.

An apparatus for treating radio tube parts in accordance with this invention, and shown by Way of example in the drawing, comprises a tubular heating chamber i, similar to that of a mufile furnace, with means for freely circulating steam over and around the parts in the chamber. The chamber is heated by a heating unit 8 shown as an insulated resistance heating coil surrounding the chamber. Steam admitted at the inlet port 2 near the center of the furnace structure travels to the right along the chamber and is exhausted at the outlet port 3. The tube parts are preferably placed in the chamber in open ended cylindrical carriers or boats 4, shown in the figures as tubes of a diameter slightly less than the internal diameter of the furnace chamber and closed at one end with a screen, and are loaded end-to-end in the chamber. To distribute the steam uniformly throughout the cross-section of the chamber, perforated disc 5 is positioned transversely across the chamber adjacent the inlet port 2 and is secured by rod 6 to imperforate disc I, which closes the left hand end of the chamber. The right-hand end of the chamber is closed by imperforate disc 1 attached by rod 6' to perforated disc 5'. These disc assemblies indicated as A and B, respectively, are of such a diameter as to slidably fit inside the chamber wall.

In operation, the tube parts to be treated are placed in carriers 4 and are slid end-to-end into the right-hand end of the chamber, the outer end of the chamber then being closed by disc 1'. The chamber and its contents are raised to a temperature of about 350 C. by passing current through the heating coil 8, and saturated steam, preferably evolved from pure Water, is introduced at the inlet port 2 under slight pressure to produce a current of steam through the chamber. It has been found that tubes made with metal parts carbonized and steam treated at 350 C. for about minutes in accordance with our invention have good cathode emission and low gas content and prolonged useful life.

It has been found undesirable to expose the tube parts to the atmosphere while heated to the temperature of 350 C., and that it is advantageous to lower the temperature of the parts gradually in the presence of steam to about C. before removal from the furnace. To eliminate loss of time in raising or lowering the temperature of the furnace between batches of tube parts, the furnace is provided, in accordance with a further feature of the invention, with a second chamber 9 of the same diameter and length as chamber 1 and coaxial therewith. This chamber has a steam inlet Ill, steam outlet II, and heating element 12, similar in dimensions and construction to the conjugate portion of the furnace, and has disc assemblies C and D at the inlet and outlet ends, respectively, of the chamber to uniformly distribute the steam throughout the cross-section of the chamber. After the 350 treatment in chamber I, the cylindrical carriers with their contents and disc assemblies A and B are pushed to the left to bring assemblies A and B into the position of assemblies D and C, respectively. Immediately a new batch of parts may be introduced into chamber I and the temperature maintained at 350 (3., while the treated batch in the left-hand end of the furnace is held at a temperature of about 100 C. in the presence of steam. A third batch may be introduced at the right-hand end of the furnace moving the second batch into chamber 9 and the contents of chamber 9 removed from the left end of the furnace ready for use in the assembly of radio tube electrode assemblies. Insertion and removal of the carriers 4 in the furnace is facilitated by semi-circular extensions [3 and I4 of the walls of chambers I and 9.

The characteristic features of this invention may with equal facility be applied to the manufacture of continuously carbonized strips of metal. In Figure 5 a strip of metal l3, from which radio tube parts may be manufactured, is drawn through a carbonizing furnace I4 and through heating chamber l5 onto a reel 16. A continuous stream of steam is passed through chamber I5, which is heated to the optimum treating temperature by a heating coil l1. Good radio tubes have been manufactured from strip metal l3, passed through a steam chamber, having an effective steam treating length of about 12 inches, at a rate of about 8 feet per minute with the chamber heated to a temperature of 350 C. The heat applied to the strip by the heating coil is regulated to so augment the heat carried by the strip from the carbonizing furnace that substantially all of the impurities on the carbon coating are removed while the strip passes through the chamber l5.

While specific structures have been described and specific operating temperatures and schedules specified, it is obvious that the invention is not limited to the examples mentioned. It is accordingly .desired that this invention be limited only by the prior art and by the scope of the appended claims.

We claim:

1. The method of treating metal for radio tube parts comprising carbonizing the metal, heating said metal at a temperature of about 350 in an atmosphere of steam until the impurities volatile in steam are taken up by the steam, removing the steam containing the impurities, and cooling the metal in an environment free of hydrocarbons.

2. In treating metal for the manufacture of radio tubes, the process of treating the metal comprising carbonizing the metal, heating the carbonized metal to a temperature below the temperature at atmospheric pressure at which water vapor in the presence of said metal decomposes to give oxygen, exposing the heated metal to a stream of steam until volatile products are removed from the metal by the steam, and removing the steam.

3. In the manufacture of metal parts for radio tubes, the process of treating the metal comprising carbonizing the metal, exposing the carbonized metal at a temperature of about 350 to an atmosphere of steam until volatile products are removed, and cooling said metal to about 100 C. in an atmosphere of steam.

4. The method of manufacturing radio tube metal parts comprising carbonizing the parts, heating said carbonized parts-to the vaporization temperature of impurities on the carbonized parts, and passing clean steam over said parts while the parts are at said temperature for about ninety minutes.

5. In the manufacture of radio tube metal parts the process of treating the parts comprising firing the parts in a carbonaceous gas to coat the parts with carbon, heating the carbon coated parts to a temperature below the decomposition temperature of water vapor in the presence of said parts and below 350 C., passing steam over the parts while the parts are heated to said temperature until impurities in said carbon and volatile in the steam are removed, and then cooling said parts to a temperature of about 100 C. in an atmosphere of steam.

6.-The method of treating a strip of metal comprising drawing said strip through a carbonizing furnace for carbonizing the metal, and then passing said strip at a constant speed through a heated chamber, passing steam through said chamber, and regulating the speed of the strip, the velocity of the steam and the temperature of the chamber to remove the impurities on the strip volatile in steam.

CLIFFORD EDDISON. EMIL G. WIDELL. 

